Conventionally, there exist X-ray CT apparatuses in which an already reconstructed computed tomography (CT) image is displayed on a display unit. When such an X-ray CT apparatus receives an enlargement instruction to enlarge the displayed CT image, the X-ray CT apparatus reconstructs an enlarged CT image in accordance with the enlargement instruction, to cause the display unit to display the reconstructed enlarged CT image.
For example, when an X-ray CT apparatus receives an enlargement instruction, the X-ray CT apparatus reads raw data that was used in reconstruction of the displayed CT image from a storage, and subjects the read raw data to preprocessing. Then, the X-ray CT apparatus reconstructs the enlarged CT image complying with the enlargement conditions included in the enlargement instruction, using the preprocessed raw data.
However, the above X-ray CT apparatuses may require much time, because various types of processing such as preprocessing are performed from input of an enlargement instruction to reconstruction of an enlarged CT image. For this reason, the above X-ray CT apparatuses may fail to promptly reconstruct an enlarged CT image.